The invention relates to a security system for a motor vehicle. The security system has at least one sensor for sensing a status variable of the motor vehicle, a security device for disabling or enabling use of the motor vehicle, and a control unit connected to sensor and the security device. The control unit disables or activates the security device as a function of the status variable in order to prevent incorrect operation.
Motor vehicles conventionally have a security device for disabling or enabling the use of the vehicle, for example in the form of a steering wheel lock, transmission lock or immobilizer. Such a security device is usually activated when a mechanical or electronic key is pulled out of an ignition lock of the motor vehicle so that the driver automatically activates the security device when he/she leaves the motor vehicle.
However, keyless security systems are also known in which the driver carries a transmitter which, when positioned in the passenger compartment of the vehicle, automatically deactivates the security device in order to permit the motor vehicle to operate. However, the locking of the security device must not be readily activated in such a keyless security system when the driver leaves the motor vehicle because otherwise failure of the transmitter while the motor vehicle is operating would lead to undesired activation of the security device. In keyless security systems, the activation of the security device is therefore carried out by a manual user intervention, for example by the driver activating a pushbutton key in the passenger compartment of the vehicle. As an additional protection against undesired activation of the security device, the velocity of the vehicle and the engine status are sensed, the activation of the security device being disabled when the engine is running and while the motor vehicle is traveling.
A disadvantage of the keyless security system for the motor vehicle described above is that the security system must be activated by a manual user intervention in all cases. This entails the risk of the motor vehicle remaining unsecured if the driver forgets to activate the security system when leaving the motor vehicle.
It is accordingly an object of the invention to provide a security system for a motor vehicle which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which it is impossible to forget to activate the security device when leaving the motor vehicle.
With the foregoing and other objects in view there is provided, in accordance with the invention, a security system for a motor vehicle having an engine. The security system includes at least one sensor for sensing a status variable of the motor vehicle, a security device for disabling and enabling use of the motor vehicle, and a control unit having an input connected to the sensor and an output connected to the security device. The control unit disables and activates the security device in dependence on the status variable, to prevent an incorrect operation of the motor vehicle. The control unit has a logic circuit that not only blocks the security device for preventing activation, in dependence on the status variable, but also activates the security device in dependence on the status variable, independently of a user intervention.
The invention involves the general technical teaching of automatically activating the security system of a motor vehicle as a function of one or more status variables of the motor vehicle, the status variables being measured by sensors. The sensing of the status variables of the motor vehicle is used here therefore not only to prevent incorrect operationxe2x80x94as is the case in the keyless security system described abovexe2x80x94but also permits automatic activation of the security device independently of a manual user intervention.
The security system according to the invention preferably has a plurality of sensors which each sense a status variable of the motor vehicle in order to activate or deactivate the security device as a function of the status variables. The evaluation of a plurality of status variables provides the advantage that an undesired activation of the security device can largely be prevented because the output signals of the sensors are logically connected to one another. Preferably, the output signals of the sensors are subjected here to a plausibility check in order to prevent an undesired activation of the security device in the event of a failure or a malfunction of one or more of the sensors.
In the preferred embodiment of the invention, one of the sensors is a transmission sensor that senses the gearshift setting of a manual or automatic transmission. The invention is based here on the knowledge that, before leaving a motor vehicle, the driver of the motor vehicle selects the first gear speed in a manually-shifted transmission and the park setting in an automatic transmission. For this reason, the activation of the security device is preferably enabled only if the first gear speed or the park setting is selected.
Furthermore, a clutch sensor, which senses the setting of a clutch pedal of the motor vehicle, is preferably connected, the activation of the security device being preferably enabled only if the clutch pedal of the motor vehicle is not activated.
Moreover, a brake sensor is preferably provided which senses the setting of a parking brake of the motor vehicle, the activation of the security device being preferably enabled only if the parking brake is activated.
In addition, in the preferred embodiment of the invention, at least one door contact sensor or at least one door handle sensor is provided, the activation of the security device being preferably enabled only if the door contact sensor or the door handle sensor is activated.
Furthermore, a velocity sensor is preferably provided which measures the velocity of the motor vehicle, the activation of the security device being preferably enabled only if the motor vehicle is stationary and the velocity is therefore zero.
Finally, a voltage sensor that measures the electrical voltage generated by a generator of the motor vehicle is preferably connected, the activation of the security device being preferably enabled only if the voltage measured by the voltage sensor is zero.
In one variant of the invention, a signal generator is also provided in order to signal the activation status of the security device to the driver. The signal generator can be, for example, a visual signal generator in the form of a monitoring light or an acoustic signal generator, for example in the form of a warning buzzer. The signal generator is preferably activated by a logic circuit that is additionally connected to at least one of the sensors in order to activate the signal generator as a function of the status variable or variables. The logic circuit is preferably connected to the transmission sensor and the clutch sensor in order to also activate the signal generator when the security device is activated if the clutch is depressed or the gearshift lever is moved into the idling setting or neutral setting.
In one variant of the invention, a manual activation element is additionally provided in order to be able to activate the security device independently of the status variables measured by the sensors, which is important in the event of a sensor failure, for example.
The security device is preferably deactivated by a transmitter that transmits an encoded signal to a receiver in the motor vehicle as long as the transmitter is located in the passenger compartment of the vehicle or at a predefined distance from the motor vehicle.
In accordance with an added feature of the invention, the control unit has a first AND gate with a first input connected to the velocity sensor and a second input connected to the voltage sensor to enable an activation of the security device only when the motor vehicle is stationary and the engine is switched off.
In accordance with an additional feature of the invention, the control unit has a second AND gate with a first input connected to the transmission sensor and a second input connected to the clutch sensor and the second AND gate enables the activation of the security device only if a gear is engaged and the clutch pedal is not activated. The control unit has a third AND gate with a first input connected to the door sensor and a second input connected to the clutch sensor and enables the activation of the security device only if the door sensor is activated while the clutch pedal is not activated. The control unit has a fourth AND gate with a first input connected to the brake sensor and a second input connected to the first AND gate. The fourth AND gate enables the activation of the security device only if the parking brake is activated and the motor vehicle is stationary and the engine is switched off.
In accordance with another feature of the invention, the security device includes at least one safety device being a steering wheel lock, an immobilizer, an alarm system and/or a transmission lock.
In accordance with a further feature of the invention, a switching element is connected to one of the inputs of the control unit in order to activate the security device manually independently of an automatic activation by the sensors.
In accordance with another added feature of the invention, a sample-and-hold element is connected to the output of the control unit in order to maintain the activation status of the security device after an activation, independently of the status variables.
In accordance with another further feature of the invention, the sample-and-hold element has a resetting input in order to be able to deactivate the security device again after the activation.
In accordance with a concomitant feature of the invention, a receiver is connected to the resetting input. The receiver is part of a transmitter which permits keyless operation of the motor vehicle.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a security system for a motor vehicle, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.